Convert search to HMVC

Conflicts:
	components/com_kunena/site/models/search.php
Improve search HMVC

Conflicts:
	components/com_kunena/site/layout/search/results.php
	components/com_kunena/site/models/search.php
Only use new HMVC on HTML, skip other formats for now
Merge pull request #1958 from mahagr/feature-hmvc

Convert search to HMVC